Method of preparing catalyst for polymerization of aliphatic polycarbonate and method of polymerizing aliphatic polycarbonate using same

ABSTRACT

Disclosed is a method of preparing a catalyst for polymerization of an aliphatic polycarbonate including oxidizing a dicarboxylic acid precursor and a zinc precursor under a pressurized condition, and a method for polymerizing the aliphatic polycarbonate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for preparing a catalyst forpolymerization of aliphatic polycarbonates and a method for polymerizingaliphatic polycarbonates using the catalyst, and more particularly, to amethod for preparing a catalyst for polymerization of an aliphaticpolycarbonate exhibiting high catalyst activity.

2. Background of the Invention

Carbon dioxide from industrial activities, among atmospheric pollutants,has been known as one reason for climatic change according to UNFCCC, sovarious studies to reduce the amount of carbon dioxide produced havebeen undertaken all around the world. Therefore, in order to protect theenvironment and to use carbon dioxide, a method in which an epoxidereacts with carbon dioxide as a carbon source in the presence of azinc-included catalyst to prepare an aliphatic polycarbonate hasattracted attention.

The aliphatic polycarbonate is able to form a film or a particle, andhas uses in many areas such as for ceramic binders, evaporation mold,and adhesives. However, this method has a low yield because of lowcarbon dioxide reactivity. Accordingly, it is difficult to useindustrially, so it is required to prepare a catalyst exhibiting highefficiency for increasing the yield of the aliphatic polycarbonate.

Inoue teaches a method of polycarbonate production from carbon dioxideand epoxide in U.S. Pat. No. 3,585,168.

The Inoue catalyst system was prepared by the reaction of a diethylzinccatalyst with materials containing active hydrogen compounds, e.g.,water, dicarboxylic acid, or dihydric phenols, and the typical catalystproductivities ranged from 2.0 to 10.0 grams of polymer per gram ofcatalyst used. The catalyst has shortcomings associated with use andstorage, because of stability and sensitivity to moisture and to othercatalyst poisons, and it has a low yield, so it has been required tostudy other catalyst systems.

Zinc dicarboxylic acid esters (Polymer J. 13(4), 407(1981)) reported bySoga have also been described as effective catalysts forcopolymerization of carbon dioxide and propylene oxide, and since theseare stable materials with none of the handling problems associated withdiethylzinc, they represent interesting candidates for a practicalcommercial catalyst system.

Motika (U.S. Pat. No. 5,026,676) teaches a method for preparing zincdicarboxylic acid ester in which zinc oxide reacts with dicarboxylicacid in the presence of an organic solvent. Glutaric acid and adipicacid produced catalysts with higher activity than the known zincdicarboxylic acid ester catalysts, and the catalyst production is about2 to 26 grams of the aliphatic polycarbonate per gram of catalyst.

It has been reported that zinc dicarboxylic acid ester can be preparedby using various zinc precursors and high crystallinity increases yieldper gram of catalyst (Ree. et al. J. Polym. Sci: Part A: Polym. Chem.37, 1863 (1999)).

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method ofpreparing a catalyst for polymerization of an aliphatic polycarbonatehaving high efficiency.

It is another object of the present invention to provide a method ofpolymerizing an aliphatic polycarbonate using the catalyst, with a highyield.

These and other objects may be achieved by a method of preparing acatalyst for polymerization of an aliphatic polycarbonate, includingoxidizing a dicarboxylic acid precursor and a zinc precursor under apressurized condition.

In order to achieve these objects and others, the present inventionprovides a method of polymerizing an aliphatic polycarbonate, includingcopolymerizing alkylene oxide and carbon dioxide in the presence of acatalyst prepared by oxidizing a dicarboxylic acid precursor and a zincprecursor under a pressurized condition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are optical microscope photographs of a catalyst accordingto Example 1 of the present invention; and

FIGS. 3 and 4 are SEM photographs of the catalyst according to Example 1of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a method of preparing a zinc-includedcatalyst having good efficiency for preparing an aliphaticpolycarbonate.

The inventive procedure includes oxidizing a dicarboxylic acid precursorand a zinc precursor under pressurized condition. One example of theprocedure is shown in the following reaction formula 1. As shown inreaction formula 1, the dicarboxylic acid precursor oxidizes under apressurized condition, to prepare a complex of the compound with a zincprecursor (hydrothermal reaction)

where R is (CH₂)_(x) and where x is an integer of 0 to 10, e.g., phenyl,or naphthaloyl.

The useful zinc precursor may be anhydrous zinc acetate, zinc hydroxide,zinc nitrite, zinc perchlorate hexahydrate, zinc oxide, zinc sulfate,zinc acetate dihydrate or zinc nitrate hexahydrate. Preferred are zincsulfate, zinc oxide, zinc perchlorate, zinc nitrite, zinc hydroxide, orzinc acetate dihydrate, which are readily complex with ligands.

The dicarboxylic acid precursor may be a compound in which halogen,cyanide, aldehyde, or an anhydrous functional group are presented atboth terminal sites, and examples are aliphatic compounds withdihydroxyl groups, aromatic groups with dihydroxyl groups, dihalogenatedalkanes, dihalogenated aromatic compounds, aliphatic compounds withdicyanide groups, aromatic dinitrile compounds, aliphatic compounds withdi-amide groups or aliphatic compounds with dialdehyde groups.

Examples of the aliphatic compound are ethyleneglycol, propanediol,butanediol, pentanediol, hexanediol, octanediol, decandiol, ordodecandiol; and examples of the aromatic compounds with dihydroxylgroups are 1,2-benzenedimethanol, 1,3-benzenediemethanol,1,4-bezenedimethanol, 1,2-naphtalene dimethanol, 1,3-naphtalenedimethanol, 1,4-naphtalene dimethanol, 1,5-naphtalene dimethanol,1,7-naphtalene dimethanol, 1,8-naphtalene dimethanol, 2,3-naphtalenedimethanol, 2,5-naphtalene dimethanol, 2,6-naphtalene dimethanol, or2,7-naphtalene dimethanol. In addition, examples of the dihalogenatedalkanes are 1,2-dibromoethane, 1,2-dichloroethane, 1,3-dibromopropane,1,3-dichoropropane, 1,4-dibromobutane, 1,4-dichlorobutane,1,5-dibromopentane, 1,5-dichloropentane, 1,6-dichlorohexane,1,6-dibromohexane, 1,8-dibromooctane, 1,8-dichlorooctane,1,10-dichlorohecane, or 1,10-dibromodecane; and examples ofdihalogenated aromatic compounds are α,α′-dichloro-o-xylene,α,α′-dichloro-m-xylene, α,α′-dichloro-p-xylene, α,α′-dibromo-o-xylene,α,α′-dibromo-m-xylene, or α,α′-dibromo-p-xylene. Examples of thealiphatic compounds with dicyanide groups are oxalnonitrile,malononitrile, succinonitrile, glutaronitrile, adiponitrile, 1,5-pentanedinitrile, 1,6-hexane dinitrile, 1,8-octane dinitrile, or 1,10-decanedinitrile; and examples of the aromatic dinitrile are 1,2-benzenedinitrile, 1,3-benzene dinitrile, 1,4-benzene dinitrile, 1,2-naphtalenedinitrile, 1,3-naphtalene dinitrile, 1,4-naphtalene dinitrile,1,5-naphtalene dinitrile, 1,7-naphtalene dinitrile, 1,8-naphtalenedinitrile, 2,3-naphtalene dinitrile, 2,5-naphtalene dinitrile,2,6-naphtalene dinitrile, or 2,7-naphtalne dinitrile. Examples of thealiphatic compounds with diamide groups are oxalic imide, malonic imide,succinic imide, glutamic imide, adipic imide, 1,5-diimide pentane,1,6-diimide hexane, 1,8-diimide octane, or 1,10-diimide decane; andexamples of the aliphatic compounds with dialdehyde groups are oxalicdialdehyde, malonic dialdehyde, succinic dialdehyde, glutaryldialdehyde,adipic dialdehyde, 1,5-dialdehydepentane, 1,6-dialdehyde hexane,1,8-dialdehydeoctane, or 1,10-dialdehyde decane.

The dicarboxylic acid precursor is more preferably pentanediol,hexanediol, 1,5-dibromopentane, 1,5-dichloropentane, 1,6-dichlorohexane,1,6-dibromohexane, glutaronitrile, adiponitrile, glutaamide, adipicamide, glutarylaldehyde, or adipic aldehyde.

The equivalent ratio between the zinc precursor and the dicarboxylicacid precursor is preferably 1:10 to 10:1, and more preferably 1:3 to3:1. The oxidation is performed in water, preferably distilled water andthe mixture is dissolved in water followed by addition to a pressurizedreactor. The amount of the precursors is 0.1 to 50 volume % of water,and preferably 1 to 10 volume %.

Thereafter, the pressurized reactor is heated to a temperature between120 and 180° C. whereby the distilled water is vaporized. The heating iscontinued for 1 to 40 hours, and preferably 20 to 40 hours to prepare azinc-included catalyst, zinc dicarboxylic acid ester. It is generallyknown that such a hydrothermal synthesis makes products with uniquecrystallinity which cannot be obtained from general procedures.

The resulting catalyst is washed to increase purity. The pressurizedreactor is cooled to room temperature and filtered to obtain atransparent mono-crystal precipitated material followed by washing withdistilled water and acetone several times. The product is dried in avacuum drying oven at room temperature.

The inventive zinc dicarboxylic acid ester obtained from the procedureis single crystalline with a uniform surface structure derived from itsregularly arranged inner structure. Such uniformity of the surfacestructure allows it to exhibit high catalytic activity tocopolymerization of carbon dioxide and alkylene oxide when compared withthe conventional catalyst. Furthermore, such a single crystal renderspreparation of aliphatic polycarbonates with constant yield and a narrowmolecular-weight distribution during the copolymerization.

The use of water has no shortcomings associated with the use of organicsolvents such as toluene that is used in the conventional procedure, sothat the inventive procedure is environmentally friendly.

In the application, a detailed description regarding the method ofproduction of aliphatic polycarbonates using the zinc dicarboxylic acidester is not required in order to perform the present invention, becauseit is well known in the related arts, but one embodiment will be brieflyillustrated. The produced catalyst is pulverized and the pulverizedcatalyst is added to alkylene oxide. Thereafter, carbon dioxide isinjected into the mixture at a predetermined pressure (e.g. 300 psi) andthe copolymerization occurs. When the copolymerization is completed,organic solvents such as methylene chloride are added to the resultingmaterial and the obtained mixture is washed with diluted hydrochloricacid solution several times. The washed mixture is then washed withdistilled water several times and precipitation is performed usingmethanol. The precipitated material is dried in a vacuum drying oven atroom temperature to prepare an aliphatic polycarbonate.

The copolymerization is performed in the absence of organic solvents orin the presence of organic solvents such as 1,4-dioxane, toluene,benzene, methylene chloride, or cyclohexane. If the copolymerization isperformed in the absence of organic solvents, the alkylene oxide oraliphatic cyclic ester which does not participate in thecopolymerization but remains, acts as the solvent. When thecopolymerization is completed, the remaining alkylene oxide andaliphatic cyclic ester is recovered and is reused.

The produced aliphatic polycarbonate preferably has a molecular weightof 500 to 5×10⁶, which results in ready control of chemical or physicalproperties and forming properties.

The present invention is further explained in more detail with referenceto the following examples, but the examples should not be construed aslimiting the scope of the claimed invention.

EXAMPLE 1 Preparation of Catalyst

1 g of zinc perchlorate hexahydrate and 0.25 g of glutaronitrile weredissolved in 24 ml of distilled water. The resulting solution wasinjected into a pressurized reactor, the inside of which was treatedwith a Teflon film. The solution was held in the reactor at 160° C. for40 hours.

When the reaction was completed, the reactor was cooled to roomtemperature and the solution was filtered off to obtain a transparentcrystal material as shown in FIGS. 1 to 4, followed by washing withdistilled water and acetone three times or more. FIGS. 1 and 2 areoptical microscope photographs of the resultant material and FIGS. 3 and4 are SEM photographs thereof. It is evident from FIGS. 1 to 4 that thematerial has a transparent and shine crystal structure.

From the washed compound, residual solvent was removed under a conditionof 50° C./5 mmHg to obtain 0.8 g of a catalyst. The elemental analysisof the catalyst was as follows: C: 30.72%, H, 3.08%, O: 32.52%.

Polymerization of Aliphatic Polycarbonate

1 g of the catalyst was placed in a pressurized reactor in a glove boxunder a nitrogen atmosphere, and 100 ml of propylene oxide was placedtherewith. Thereafter, the reactor was pressurized to 300 psi withcarbon dioxide. The reacted mixture was kept at 60° C. for 40 hours.

When the reaction was completed, carbon dioxide was removed from thereactant and methylene chloride was added thereto. The resultingmaterial was washed with diluted hydrochloride acid solution threetimes, and then with distilled water to remove catalyst from theresulting material. Then, the material was precipitated using methanol.The obtained precipitated material was filtered and dried to obtain 50 gof propylene carbonate polymer.

Analysis using an infrared ray and nuclear magnetic resonance indicatedthat the polymer was a copolymer of propylene oxide and carbon dioxidewith a 1:1 mole ratio.

EXAMPLES 2˜4

A catalyst was prepared by the same procedure as in Example 1 exceptthat the reacted mixture was kept for times as shown in Table 1. Theyields of the catalyst are presented in Table 1.

TABLE 1 Reaction time Yield Example 2 10 hours 23% Example 3 20 hours52% Example 4 30 hours 67%

EXAMPLE 5

A catalyst was prepared by the same procedure as in Example 1 exceptthat 19 of zinc perchlorate hexahydrate and 0.5 g of glutaronitrile wereused to obtain 0.75 g of zinc glutaric ester catalyst.

Polymerization of Propylene Carbonate

Using the catalyst, polymerization of propylene carbonate was performedby the same procedure as in Example 1 to obtain 41 g of polymer.

EXAMPLE 6

A catalyst was prepared by the same procedure as in Example 1 exceptthat 0.29 g of adiponitrile was used to obtain 0.71 g of a zinc adipicester catalyst.

Polymerization of Propylene Carbonate

Using the catalyst, polymerization of propylene carbonate was performedby the same procedure as in Example 1 to obtain 12 g of polymer.

COMPARATIVE EXAMPLE 1

A catalyst was prepared by the same procedure as in Example 1 exceptthat the reaction temperature was kept at 110° C. In the procedure, awhite powder was produced and the single crystalline product was notproduced.

COMPARATIVE EXAMPLE 2

A catalyst was prepared by the same procedure as in Example 1 exceptthat zinc chloride as a zinc precursor was used. In the procedure, awhite powder was produced and the single crystalline product was notproduced.

COMPARATIVE EXAMPLE 3

A catalyst was prepared by the same procedure as in Example 1 exceptthat 20 ml of ethanol and 4 ml of distilled water were used. In theprocedure, a white powder was produced and the single crystallineproduct was not produced.

It is predicted that when amorphous compounds according to ComparativeExamples 1 to 3 are used to prepare aliphatic polycarbonate, the yieldis lower than that according to Examples 1 to 6.

As described above, the method of the present invention can prepare asingle crystalline catalyst of which high crystallinity allows anincrease in the catalyst activity, and which is useful as a commercialcatalyst for production of aliphatic polycarbonate, and the method isenvironmentally friendly without the use of organic solvent. Theobtained polycarbonate can be formed as a film or particle, and it isapplied to a ceramic binder, an evaporation mold or a binder. Inaddition, the method uses carbon dioxide as a monomer so thatatmospheric pollution and climate change due to carbon dioxide can becontrolled.

1. A method of preparing a single crystalline catalyst forpolymerization of an aliphatic polycarbonate, comprising: oxidizing adicarboxylic acid precursor and a zinc precursor under a pressurizedcondition in water, wherein the dicarboxylic acid precursor is selectedfrom the group consisting of pentanediol, 1,5-dibromopentane,1,5-dichloropentane, glutaronitrile, glutamic imide, andglutaryldialdehyde.
 2. The method of claim 1, wherein the equivalentratio of the zinc precursor and the dicarboxylic acid precursor is 1:3to 3:1.
 3. The method of claim 1, wherein the oxidation is performed ata temperature between 120 and 180° C.
 4. The method of claim 1, whereinthe dicarboxylic acid precursor and the zinc precursor are respectively0.1 to 50 volume % of water.
 5. The method of claim 4, wherein thedicarboxylic acid precursor and the zinc precursor are respectively 1 to50 volume % of water.
 6. The method of claim 1, wherein the zincprecursor is selected from the group consisting of zinc acetatedihydrate, zinc hydroxide, zinc nitrate hexahydrate, zinc perchloratehexahydrate, zinc oxide and zinc sulfate.
 7. A method of polymerizing analiphatic polycarbonate, comprising: copolymerizing alkylene oxide andcarbon dioxide in the presence of the catalyst which is preparedaccording to the method of claim 1.